1. Field of the Invention
The present invention relates to a paper feeder provided to an image forming apparatus.
2. Description of the Related Art
There are paper feeders which are provided to an image forming apparatus and configured to convey a sheet of paper (hereinafter referred to as sheet) taken out from a paper feed tray to an image formation unit by using resist rollers, the image formation unit including ink jet heads or the like.
In such a paper feeder, while being conveyed by paper feed rollers, a sheet hits the resist rollers and is held against the resist rollers temporarily. In this way, a warpage is formed on the sheet. This corrects oblique conveyance of the sheet. The paper feeder then drives the resist rollers at a predetermined time to send the sheet to the image formation unit.
The sheet causes a collision noise when hitting the resist rollers. The collision noise is loud especially in an image forming apparatus capable of a high throughput (the number of sheets printed per unit time) because sheets are conveyed at a high speed therein. Moreover, the damage on the sheet due to the collision is large as well.
To reduce the shock of the collision of the sheet with the resist rollers, it is possible to provide a shock absorbing material to the resist rollers, for example. It is also possible to provide a noise isolation cover to suppress the noise. However, adding these members causes increase in the size and cost of the apparatus.
In this respect, Japanese Unexamined Patent Application Publication No. 2009-40568 discloses a paper feeder in which: paper feed rollers convey a sheet at a first conveying speed; and the conveying speed of the paper feed rollers is decelerated to a second conveying speed, which is lower than the first conveying speed, when a detector provided between the paper feed rollers and resist rollers detects the leading end of the sheet. The second conveying speed is set based on the time point at which the detector detects the leading end of the sheet. By using this conveyance control, the paper feeder described in Japanese Unexamined Patent Application Publication No. 2009-40568 reduces the collision noise and also maintains the throughput.